This invention relates to a method for the separation of contaminants from cooling lubricants.
In the machining industry, when dry machining is not possible, oil or an oil-water mixture, preferably an emulsion, is used for lubricating and cooling the machine tools. This cooling lubricant also serves to carry the chips away to a filter system. There the chips and the cooling lubricant are substantially separated, the chips are discarded, and the substantially cleaned cooling lubricant is returned to the work process at the cutting edge of the tool.
The drive toward increasing productivity is leading, due to further improvements in tool systems, to ever-increasing cutting speeds, longer useful tool life, and also to different forms of chips. The higher performance is likewise achieved only if oil is used as cooling lubricant, with a trend toward use of higher viscosity oils.
The demands placed on the filter system are likewise increasing due to these circumstances, which means that the fineness of filtration must become ever greater, and the residual dirt content in the oil on the clean side of the filter must be reduced even further. There are filter systems which achieve these goals, but they use a filter aid for filtration, which involves purchasing and disposal costs.
Furthermore, especially in the case of new purchases, the basic rule is to give priority to reducing waste over waste disposal.
In the machining of gray cast iron, aluminum and magnesium, however, when oil is used as the cooling lubricant, the fine contaminant particle content constantly increases, especially particles having a size below about 15 .mu.m. In the case of gray iron, the graphite content predominates, and in the case of aluminum and magnesium, the predominant portion of the fine contaminants comprises extremely fine chips.
If precoated filters are not used as the primary stream filters, the ever-increasing content of fine debris in the cooling lubricant leads to clogged supply lines, sticking slides and internal walls of the machinery, plus the danger of fire in the machining of magnesium, and also the failure of internally cooled tools.
Certain filter methods also suffer from clogging by fine debris, and require ever-increasing maintenance costs.
In practice, attempts have been made to reduce this clogging at least to a supposedly tolerable level by the use of additional filters in a secondary circuit.
German Patent Application No. DE 4,205,884 discloses a method for separating dewatered waste oil in which the waste oil is said to be separated into medium-heavy mineral oils, heavy mineral oils, and solids. For this purpose the waste oil is introduced into a heating circuit, part of the waste oil is evaporated, and it is separated in a two-phase decanter into solids and into a centrifuged, clean heavy oil phase. A disadvantage of the process is high energy consumption. In the cleaning of cooling lubricants on a continuous basis, such a process is not economical.
Further, German Patent Application No. DE 4,343,609 discloses a method for processing cooling lubricants in which the cooling lubricants are heated, then decanted, and the recovered cooling lubricant is drawn off. The re-usable oil is processed by separation. This method also is characterized by a high energy consumption and is suitable only where a small amount of lubricant is to be cleaned.